A variety of combiner and divider circuits (combiner/divider circuits) operating over radio frequency (RF) and millimeter wave frequencies bands are known. One type of combiner/divider circuit often used in low power applications is a so-called Wilkinson power divider. Wilkinson power dividers are three-port devices provided from a pair of quarter-wavelength signal paths. A first end of each signal path is coupled to a first port and the second ends of each signal path correspond to the second and third ports. A signal fed to the first port is split with equal power and phase at the second and third ports. A resistive element is coupled between the quarter-wavelength signal paths. With this configuration, Wilkinson power dividers achieve isolation between the two output ports (i.e. the second and third ports in the above example) while maintaining a matched impedance condition at all ports. The quarter-wavelength signal paths can be implemented using printed circuit transmission lines, coaxial transmission lines or lumped element circuits. Since a Wilkinson power divider is made up of passive components, it is reciprocal and thus can also act as a power combiner. Thus, two signals having equal amplitude and phase fed to the second and third ports are combined at the first port.
There are power combiners that combine the outputs of multiple coaxial inputs into a single coaxial output. Some radial combiners are capable of providing high output power. However, these power combiners are typically multiple wavelengths in size at the RF frequencies of interest and are therefore incapable of supporting many applications where the power combiners must fit within a limited space such as within a lattice spacing of a phased array antenna.
Modern applications that require high RF power, also require efficiency in combining RF power using combiners. Matching a source impedance with that of an antenna has been a long standing problem for the RF power combiners in achieving this needed efficiency. In applications in which signals from a number of RF sources must be combined, impedance matching becomes a difficult problem to solve. The problem becomes increasingly more difficult with increasing numbers of signal sources. Thus, scalability in RF power combining has been a challenging problem.
Low loss performance over a wide bandwidth is a design requirement for many applications that use combiner circuits operating at RF frequencies. It is relatively difficult to provide power combiners/dividers which operate over a relatively wide RF bandwidth while at the same time having a relatively low insertion loss characteristic.